Masashi Isemura

Investigations of photo-association mechanism for growth rate enhancement in photo-assisted OMVPE of ZnSe and ZnS

Abstract The mechanism of the growth rate enhancement by xenon lamp irradiation in organometallic vapor-phase epitaxy (OMVPE) of ZnSe and ZnS II–VI semiconductors has been investigated by irradiated wavelength dependence of the growth rate. The longest wavelengths where the irradiation highly increased the growth rate were about 500 and 335–350 nm for ZnSe and ZnS, respectively, independent of the source materials used and the VI/II flow ratio. These threshold photon energies nearly corresponded to the bandgaps of the epilayers at the growth temperature, and thus we considered that carriers generated at the growing surface promoted the surface reaction, resulting in the growth rate enhancement.

Growth rate enhancement by xenon lamp irradiation in organometallic vapor-phase epitaxy of ZnSe

The growth rate of ZnSe in organometallic vapor-phase epitaxy (OMVPE) using dimethylzinc (DMZ) and dimethylselenide (DMSe) as the source materials was substantially increased by irradiation from a xenon lamp. The growth temperature was reduced from 500°C to 300°C by keeping a constant growth rate of 1~2 µm/h. Promotion of surface reaction due to irradiation was considered as one of the factors for the growth rate enhancement. The density of defects which causes deep level emissions was also successfully reduced. We suggest that this technique is very effective to obtain high-quality epilayers.

OMVPE of Zn-based II–IV semiconductors using methylmercaptan as a novel sulfur source

Abstract The use of a novel sulfur source, methylmercaptan, CH 3 SH (MSH), for OMVPE growth of ZnS and Zn(S,Se) has been developed for the first time. Gas-phase prereaction was not observed, and the growth temperature of ZnS was successfully reduced, compared with growth using dialkyl-compounds. Zn(S,Se) alloy epilayers lattice-matched to GaAs substrates had specular surface morphology, excellent crystallographic properties, and showed strong excitonic emissions but weak intensities of deep level emissions.

Use of methylselenol for organometallic vapor-phase epitaxy of ZnSe

Heteroepitaxial films of ZnSe on GaAs substrates have been grown by atmospheric-pressure organometallic vapor-phase epitaxy using a new selenium source, methylselenol, CH3SeH (MSeH). Gas-phase prereaction with a group-II source material was suppressed compared with hydride sources, e.g., H2Se. The practical growth temperature was 300–400°C, which was sufficiently lower than 500°C used in the growth with dialkyl compounds. The epilayers exhibited a fairly smooth surface morphology and good crystallographic properties. Higher quality epilayers can be expected with source repurification or synthesis via purer chemical processes.

High Temperature Growth of Non-polar a-Plane GaN Film Grown Using Gallium-Oxide as Ga Source

In this study, we reported a decrease of oxygen concentration and an increase in the growth rate of a-plane gallium nitride (a-GaN) film grown using Ga2O gas and NH3 gas. The oxygen concentration in a-GaN film was decreased with increasing partial pressure of NH3 and growth temperature. An a-GaN film with the lowest oxygen concentration of 4 ×1018 atoms/cm3 and the growth rate of 18 µm/h was obtained under NH3 partial pressure of 84 kPa at 1250 °C. We concluded that growth under high partial pressure of NH3 at high temperature can produce a-plane GaN film with a high growth rate and low oxygen concentration.

Growth of GaN layers using Ga2O vapor obtained from Ga and H2O vapor

In this study, we performed growth of GaN layers using Ga2O vapor synthesized from Ga and H2O vapor. In this process, we employed H2O vapor instead of HCl gas in hydride vapor phase epitaxy (HVPE) to synthesize Ga source gas. In the synthesis reaction of Ga2O, a Ga2O3 whisker formed and covered Ga, which impeded the synthesis reaction of Ga2O. The formation of the Ga2O3 whisker was suppressed in H2 ambient at high temperatures. Then, we adopted this process to supply a group III precursor and obtained an epitaxial layer. X-ray diffraction (XRD) measurement revealed that the epitaxial layer was single-crystalline GaN. Growth rate increased linearly with Ga2O partial pressure and reached 104 µm/h.

Dependence of polarity inversion on V/III ratio in −c-GaN growth by oxide vapor phase epitaxy

One of the issues in bulk c-GaN growth is the decrease in the diameter of crystals with an increase in thickness owing to the appearance of inclined and facets. In this study, we performed −c-GaN growth by oxide vapor phase epitaxy (OVPE). As a result, truncated-inverted-pyramidal crystals were successfully grown on dot-patterned −c-GaN substrates. The diameter of the top surface of crystals was larger than that of windows. We further investigated the dependence of the ratio of inversion-domain area to growth area (R ID) on growth temperature, V/III ratio, and growth rate. The remained results revealed that R ID decreased with increasing growth temperature and V/III ratio, and kept constant for growth rate. Additionally, an epitaxial layer on −c-GaN substrates with a growth rate of 12.4 µm/h and an R ID as low as 3.8% was obtained under an NH3 partial pressure (P NH3) of 83 kPa at 1200 °C.

Improvement of crystallinity of GaN layers grown using Ga2O vapor synthesized from liquid Ga and H2O vapor

Growth methods using Ga2O vapor allow long-term growth of bulk GaN crystals. Ga2O vapor is generated by the reduction of Ga2O3 powder with H2 gas (Ga2O3–H2 process) or by the oxidation of liquid Ga with H2O vapor (Ga–H2O process). We investigated the dependence of the properties of grown GaN layers on the synthesis of Ga2O. In the Ga–H2O process, the polycrystal density and full width at half maximum (FWHM) GaN(0002) X-ray rocking curves (XRC) at a high growth rate were lower than those in the Ga2O3–H2 process, and a GaN layer with FWHM of 99 arcsec and growth rate of 216 µm/h was obtained. A low H2O partial pressure in the growth zone improved crystallinity in the Ga–H2O process, realized by the high efficiency of conversion from liquid Ga to Ga2O vapor. We concluded that using Ga2O vapor in the Ga–H2O process has the potential for obtaining higher crystallinity with high growth rate.

Homoepitaxial growth of a-plane GaN layers by reaction between Ga2O vapor and NH3 gas

Growth of high-quality a-plane GaN layers was performed by reaction between Ga2O vapor and NH3 gas at a high temperature. Smooth a-plane GaN epitaxial layers were obtained on a-plane GaN seed substrates sliced from thick c-plane GaN crystals. Growth rate increased with increasing Ga2O partial pressure. An a-plane GaN layer with a growth rate of 48 µm/h was obtained. The X-ray rocking curve (XRC) measurement showed that the full widths at half maximum (FWHMs) of GaN with the incident beam parallel and perpendicular to the [0001] direction were 29–43 and 29–42 arcsec, respectively. Secondary ion mass spectrometry (SIMS) measurement revealed that oxygen concentration decreased at a high temperature. These results suggest that growth of a-GaN layers using Ga2O vapor and NH3 gas at a high temperature enables the generation of high-quality crystals.